The biggest hurdle in making Linux 3D game repo is the Software Patent Law, there are many binaries used when one compile a 3D game, it will take some time to have a complete Open Source/Free libs for game programming.

This is why I asked that you must read about Software Patent Law, "even if your software is GPL you might be using binaries/concept in your software, those are protected by Patent Law, and eventually you will be caught under Software Patent Law", you need to read Richard Stallman's Talk on Patent Laws http://news.zdnet.co.uk/software/0,1000000121,2107481,00.htm also you must visit http://gnu.org there is a lot about the issue.

I hope these will clear the difference of a GPL and software Patent Law.